Infrared missile fire control system



May 12, 1964 Distance in a Direction Transverse To 'The Line of Flight of The Target K. N. SATYENDRA 3,133,188 INFRARED MISSILE FIRE CONTROL SYSTEM Filed Sept. 27, 1957 Stick Movement Fig.|.'

I3 Aircraft 2Q. 27 ,25

Heading Steering M 2 3 C5 d) Signal I Steering Fire and obtaining Signals I Break Away Means 4 8 Indicator SighI Line 2%(Log i='r)E|=,+i= {M51324 i T T I2 32 T An ular 34 j g l 2 Comparator 2o F +F (w) y /33 7 Mach Density Number Ratio Altitude 4 22 28 ,23 at (Log Pr) Received 1 IR Power n Pr) C Line of Sight At I Launching Target x 7 I y Distance in a Direction Corresponding To The Line of Flight The Target Missile Launcher U t d t tes P tent 3,133,188 1 INFRARED MISSILE FIRE CONTROL SYSTEM Kudumalakunte N. Satyeudra, Glen Burnie, Md., asslgnor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed Sept. 27, 1957, Ser'. No. 687,598 13 Claims. (Cl. 235-615) invention relates to fire control systems and more particularly to infrared fire control systems particularly adapted for launching air-Ito-air guided missiles. 7 1-Heretoforc,"-infrared t racking'systemshave not been successfully applied to an infrared fire control system for interception of airborne targets and'launching of guided missilesitoward these targetsrfor-"the reason that no accurate methodr'of extractingrange information from the received infrared energy has as yet been developed, and as will be readily understood, the guided missilemust not be launohed t'rom a distance exceed-ing its useful range, nor from a distance less than its minimum firing range;

The apparatus of the instant invention provides a simple method of operation for an accurate missile fire control system which does not depend on the evaluation of range information. The apparatus of the instant in vention supplies all the other information normally sup plied by a fire control system including steering information, signals for missiles with ti good degree of hit probability, and signals for breaking, off the combat in order to safeguard the aircraft and the pilot from collision with the enemy target. 1

' [In the apparatus of the instant invention an infrared scanner mounted on the pursuit aircraft searchm, locks on, and tacks a target and provides informationregarding'the line of sight betweenvthe aircraft and the target to a heading indicator, and the indication thereon is utilized by the pilot in controlling the stickto follow a pure pursuit course. From the-infrared scanner, angular rate information is also obtained: and this angular rate i information is employed in computing a signal in accordi ance'with the Mach number of the aircraft speed and the 40 density ratio in=acodrdance with thelaltitude ofthe aircraft for use in a signal comparator. From the'infrared scanner a" signal representing received-infrared power "is also obtained and utilized in computing a time derivative signal which is a function of the logarithm of the received power, for application torthe comparator, and fro-mthe comparator Jan -additional signal is obtainedwhich applied to a lfire and breakaway indicator which indicates to the pilot when the pursuit aircraft is within firing range, H- and when the pursuit aircraft has gotten too close to the 50 target and should break away to seek another target or follow areattack course. 11;; q; Accord-ingly,'the primary objective of the invention is j to provideanew. and improved infrared missilefire-con I trol system. V l 55 1 a, Another object is to provide a new and improved infraredjmissile fire control system particularly suitable for launchingair to-air guidedvmissiles. 7 a A furtherobject is topr'ovidea newand improved in-, frared missile-fire control system in .fwhich' the necessity for accurate range information is eliminated ap'e' al oftheifollowing specification when raid in a nectioniwith the accompanying "drawinggin which 7 is a scheniaticldiag ram, in block form, of

missile treads-eel system according to the ferred embodiment of the invention,- and i I is a graph illustrating theoperaticnof "p tusro 1.} r

In FIG. ,l,;to;which part1cularattention "is, directed,

there is'shown at 10 on infrared scanning apparatus which 5 ,-s ra 1y e r e se h t iisiapplied 1b 7 vice shown 11" block to ni 3,133,188 Patented May 12, 1964 may be of any convenient design, the scanning and searching apparatus 10 being constructed and arranged to lock on and track a target. The infrared detector portion of 10 may include, if desired, a PbS cell. For a fuller discussion of infrared detector devices reference may be had to Detection and Measurement.of'lnfraredfl by Smith, Jones, and Chasniar, I Oxford Clarendon Press, 1957. The angular rates of the line of sight to the 'target with respect to the longitudinal axis of the aircraft are measured in a convenient manner as by gyroscopes suitably mounted with respect to the gimbal axes of the in frared seeker of the scanning apparatus, and the 'scaler value it of the total sight line angular rate is measured or obtained through a summing device of any convenient design and indicated in block form at 1.1, the angular rate computerv .11 bein-goperatively connected to the" infrared scanner" 10' by means 9 and 12. Assuming tori'purposes of illustration that device 10' .suppliestwo angular rates measured in two mutually perpendicular directions, ap-' paratus '11 may obtain a total angular rate by a process including summing the squares of the rate sig- 3 7 350-353. There is also provided from the infrared scanner 10 information regarding the sight line angle which may include two sight line angle signals giving measurements of sight line angles in two mutually perpendicular planes both passing through the longitudinal axis of the aircraft, and steering signals-are obtained as by apparatus shown in block form at 113 and applied to an aircraft heading indicator 14which may be of any convenient design such, for example,- as an optical device or a cathode ray device. Let it be assumed that lead means 7 and 8 provide two signals representing sight line angles, there are ob tained at: 13 steering signals forj positioning. a target indication 5 on aziinuth scale 4 and elevation scalef3' of in-' dicator 14. The pilot of the aircratt utilizes the signal on indicator 14 to operate the stickito provide that the aircraft follows ia pure pursuit l The aforementioned angularrate signalw. is applied by lead means 32 to computing "apparatus which may be of any convenient design and show'nin block form zit-15, com:

puting apparatus 15, having switching means ldof any convenient design for settinginor removing a multiplying factor forone term of a firefcontrol equation, for reasons which will becomehereinafter more clearly apparent.

Supplied to the-computer'-15' in addition to'the angular rate signal or are signals corresponding to.the.Mach number of the aircraft speedlobtained from" any suitable source. 17, a signal correspond-inglto density mud in accordance, with the altitude of theaircraftiand obtained trom any suitable source .l'8, and under some conditions a signal corresponding to the; l from any suitable source de of the aircraft and obtained 19." e-. output of computer lead mean 4 to 'a': signal comparator die; and generallj designated .20;-

the signal eomparator zo eingipmvided be hereinaftermore clearly apparent;

'Ifhe signal on lead figgcorresponding to rate. I (to) may be either a voltage or current, asd ired -Compu-ter 15 mayinclude simple" addition, subtraction, jrnulti- Computers by Korn and for reasons f to" where M =Mach number, and

where o.4j o bi name is below 28,000 feet 7 Firing signals can be expressed in the form in which R=range between launcher and target 1 E =range rate I .7

w=angular rate of line of sight I F and F are functions of launcher speed, altitude, missile aerodynamics, missile time of flight, etc.- i,

As aforementioned, the apparatus of the'instant invention obviates the necessity for computing accurate range information. Furthermore, in the apparatus of the instant invention, *F and F may be simplycomputed in terms of Mach number and density ratio after certaln constants havebeen empiricallydetermined or statistically selected in accordance with known missile time of flight and/or known minimum useful missile terminal velocity characteristics of the selected missile. For a more detailed discussion of these :factors reference may be had to Aerodynanriics, Propulsion, Structures and Design Practice, by Bonney, ZUCIOW, and Besser'en'Van Nostrand Coi, Inc.,'1956. I a V Y In accordance with a first setting of switch 16, and as- 1y designated 23', for computing a signal corresponding d 7 7t (10g P7) This last-named signal is applied by lead means 33 to V comparator 20. A signal having a value corresponding can be conveniently obtained at 23 by first applying the suming for purposes of illustration certain missileaerodynamic values, the values of F and F may be computed as follows:

is rn computed according to the second switch setting, and

where a=density ratio atoperating altitude. 7

In accordance with the second setting of switch 16, and assuming the same missile aerodynamic values, F and F may be computed as follows: u

v where a ).4 or. the altitude is beloW 28,O0 Ofeet; and, as

The may lye eliminated from the computation where desired to simplify the computing apparatus without too great a loss of accuracy; 7

d I 5i (log P; V

signal'on lead 28 to a logarithmic amplifier such for example as'one similar to that described in :an article by Chambers and Page entitled High Accuracy Logarithmic Receiver, Proc. I.R.E., vol. 42, N o. 8; page :1307, August I 1954. The output of. the logarithmic amplifier included in 23 may then be applied to a difierentiator circuit, such asone similarto those described in Electronic Instruments by Greenwood, Hold-am, and Macrae, vol. 21, Radiation Laboratory Series, McGraw-Hill Book Com- 112111351948, pp. 64e78. i

- The received infrared power, if'the range-dependent attenuation of the atmosphere is neglected as it may be especially at high. altitudes, is given by the expression v Rrate of ehangein range a The ratio of the last two expressionsfgives ELTJZ 1 at" a a In the-subject apparatus, the receivedpower is preferi ably measured by a logarithmic receiver included in 23,

. and the time derivativeof this quantity is given by As aforementioned, the constantsnn the ya tisjei F and F are empirically. determined in accordance with .1

the characteristics of the actual missiles selected to vbe" used, and 1.6 is the estimated closing speed in F -1 R, will be greater-in the second switch setting than Mach between a chosen bomber target and a chosen fighter aircraft flying toward each, other. Because M 1.6 will always be less than unity-for the-selected fighter wvhich has-a maximum speedof Mach l, the .val-ueQf;

it is inthe first setting of switch 16, assuming"; andgt i are unchanged.

As aforementioned, the imaginable also pro vides 'by way of conducting means 21 a signal which is v itself proportional to received I -R" power, or can be utilized. by'apparatus '22, of; any convenient design, to; I provide on output lead 'means-ZS a signal proportional to received infrared power. From the'apparatus 22 asigna'ln is suppliedby'le'ad means 28 to computing apparatus of any convenient design, shown in block form-and general the following equation Twice the-reciprocal of the'last-nained equation is the quantity: v I

H I it The missiles are successfully launched .bylthepilioflwho by the use of, comparator 20 compares thequantities 0i ,1: V g i V As aforementioned, the-left hand side of this last stated a equationj smeasured from the receivedinfrared power whereas the righthandlsidegof the-equation is computed from the altitude ordensity -rati o, fighter speed,'and infrared seeker gimbal axle ratelmeasurement's. Thecom I 'parisonof the instant quantities of the two sides offthe equation is made. by comparator 20, which. supplies ,sig-

nals'by conducting; means 24 to a fire and break-away in: 'i

'dicator which may have green andredflights26 and" -27, respectively, for indicating to'the pilot when he comes" within firing rangejand when he has approachedfto with- I In FIG. 2, the curves illustrate the zones for a typical '75 in a dangerous distance and should break away.

missile thav'ingfits own guiding system, for: example,

band radar homing apparatus. The radar apparatus on the missile may be if desired of the passive detection type depending upon radar illumination of the target by a radar transmitter located on the pursuit aircraft or missile "launchersame lineyafter the period insertThe coordinate scales of FIG. 2 represent distances from the target, in directions parallel to and transverse to the line of flight 30 of the target T. All of the contour curves of FIG. 2'lie in the same plane, a horizontal plane passing through the target. It should be understood that similar contours could be provided for attack in any other plane rotated 36O degrees about target line of flight30,

but that the-other contours in non-horizontal planes might a not bespaced in the same manner as those of FIG; 2 be if cause of gravity forces aiding or opposing the normal aerodynamic range of the guided missile. Curve A indi- 'catesthe: maximum aerodynamic range of a typical missile chosen for explanatory purposes; curve or'contour B represents the area covered by the In-range signal, when fora first switch position or setting of switch 16 and resulting values of F and F curve C represents the minia mum range of the selected missile depending upon such factors as safe fuse'arming time, minimum time required for activation of missile control surfaces, and soforth; curve D represents the final launch signal, computed according to the following equation:

% g P7)= F +F (w) I "*E'It will be noted that distance. (y) is smaller than dis- V tahce (-x) measured on targetfiight path 30 because of the direction'of movement of the target from right to 5 left as seen in FIG. 2. a t Y Assume for purposes of description that the interceptor aircraft is tracking a targetin a pure pursuit mode with the-computer 15 having its switch 16 in the first setting.

- ;;Itmay be noted that the value of a' signal on lead means i '33 corresponding to I i a (log Pr) 7 .maybe expectedto increasefin amplitude as the range between target and pursuit missile launcher aircraft defconstructed and'arranged toshowthat thedifference' g lZi-[F'H fllwfl is negative. i i

, V As" the pursuit 5 the amplitude of thesignal corresponding to e d v z it e 20k "contours' B andDof FIGZ. I1

Assoon-as 6 changes sign (or soon thereafter, orisoon switch 16- to its seco n'd' setting" thereby. increasingfthe creases. While the pursuit'aircraft is outside of contour I B, the right hand side of the equation hereinbelow'is greater than the left hand side, and the indicator 25 is.

aircraft approaches nearer the target,

after-.fir'ing the first missile), thepilot o'r' gunner changes.

value: of F The pilot mayficojn-tinue to fire. missiles succession the indicator. 25 ,shows that e-has changed .sign-fo'rasecond time which may be indicated by enermeans that the interceptor aircraft has crossed curve or contour D of FIG. 2. The interceptor must break away and go after a second target or prepare for reattack.

Whereas the invention has been shown and described with reference to its use on aircraft, it should be under- .stood that the apparatus could be at a fixed location; the necessity for supplying-Mach number to the computer 15 being eliminated.

While the invention has been shown and described with reference toan embodiment thereof which gives satisfactory results, it should be understood that modifica tions may be made and equivalents substituted without departing from the spirit and scope of the invention.

I claim as my invention: 1. In an infrared missile fire controlsystem, in combination, first computing means responsive to infrared radiation received from a target for computing a first signal having a value corresponding to the time derivative of the received infrared power d. tlog P1) second computingmeans for computinga second signal having a value corresponding to F +F (w), where F and F are selected functions of launcher speed, missile aerodynamic characteristics, missile maximum range and at least one atmosphere condition in accordance with altitude and density ratio, and w is the scalar value of the sight line'rate between the launcher position and the target, and firing indicating means operatively connected to both said first and second computing means and hav- 'ing said first and second signals appliedthereto, said'fi'ring indicating meansfbeing constructed and arranged to give a firing indicationfl when said first and second signals attain 'equalvalues; i i Y 2. In an infrared missile fire control system, in combi:

nation, first computingmeans responsive to infrared radiation received from a target for computing a first signal having a value corresponding to the time derivative of the received infrared power instant sight-linerate betweenfth'e launcher position and,

structed and arranged toprovide a first signal 'havinga I value corresponding to, the derivative of thereeeived infrared power 7 the target, said'second computing means including switch ing means for selecting one of two values of. F and firing indicating means-operatively connected tofb'othfsaidfirst and second computingl means and havingjsaid first and second signals j applied thereto, said firingindicating means being "c'onstructedand arranged to give a' firing'indication when said. first and second signals attain equal values.

"isfsile fire control system ,use on aircraft,

combination, infrared' tracking means adaptedj'to lock on a target; said infrared tracking me anspbe'ing con said infrared trackirigiineans'being constructed and arrangedQto-pr vide econd signal corresponding 9 the sca1er;value. ofoflh instant sightiliiierate bet'w jth f launcher aircraft and target, computing meansopera i vely-corinectedtoisaid infrared .tracking'm'e'aiis arid having i i ed theretofsaid.computing rne'anel computing a thi'rdsign'alfjhaving 5a value corresponding to said second signal app bination, computing means responsive to infrared radiation'received from a target for providing a firing signal is the time derivative of the received infrared power, to is the scalar value of the instant sight line rate between the launcher aircraft and target, and F and F are selected 7 functions of launcher speed, missile aerodynamic characteristics, missile maximum range, and at least one atmosphere condition in accordance with altitude and density ratio, and indicating means operatively connected to said computing means and having said firing signal applied thereto, said indicating means utilizing the to provide a firing indicator]. 5. In a missile fire control system for use in combination, infrared tracking means adapted to lock on a target, computing means operatively. connected to said tracking means and responsive to infrared radiation received from the target for providing a firing signal when g (log P7") =F F (co) where I d 1 tlog Pr) firing signal 7 on aircraft,

is the time derivative of the received infrared power, to

- is the scalar value of the instant sight line rate between the launcher aircraft and target, and F -and F are selected functions of launcher speed, missile aerodynamic characteristics, missile mam'mum range, and at least one atmosphere condition in accordance with altitude and density ratio, and indicating means operatively connected to said computing means and'having said firing signal applied thereto, said indicating means utilizing the firing signal to provide a firing indication.

firing signal applied thereto, said indicating means utilizing the firing signal to provide a firing indication.

7, In an aircraft missile fire control system, in combination, infrared tracking means adapted to lock on a target, said infrared tracking means being constructed and arranged to provide a first signal having a value corresponding to the time derivative of the received infrared power d 32 (log P1) computing means operatively connected to said infrared tracking means andhaving said first signal applied thereto, means operatively connected to said infrared tracking means and to said computing means for supplying to said computing means a variable second signal corresponding to the instant value or" a variable to which is the scalar value of the instant sight line rate between the launcher aircraft and target, said computing means, being constructed and arranged to provide a firing signal when where F and F are selected functions of launcher speed, missile aerodynamic characteristics, missile maximum range, and at least one atmosphere condition in accordance with altitude anddensity ratio, and indicating means operatively connected to said computing means and having said firing signal applied thereto, said indicating 'rneans utilizing the firing signal to provide a firing indication. 1

' 8. In an aircraft fire control system for use with a homing type guided missile, in combination, infrared tracking means adapted to lock on a target, target position indicator means operatively connected to said infrared tracking means for indicating to the pilot of the aircraft the position of thetarget with respect to the instant heading of he aircraft, computer means, said infrared tracking means being constructed and arranged to provide to the computer means a pair of signais corresponding respectively to the time derivative of the received infrared power aind to the scalar value no of the instant sight line rate between the'launcheraircraft and target, said computer means being constructed andarranged to provide a firing where'F and F are selected functions of launcher speed,

missile aerodynamic characteristics, missile maximum range, and at least one atmosphere condition in accor 6. In an-aircraftmissile fire control system, in combination, computing means responsive to infrared radiation received from a target, means operatively connected tosaid computing means for supplying thereto a variable input corresponding to the instant value of a variable which is the scalar' value of the sight line rate between the launcher aircraft and target, said computing means being responsive to infrared radiation received from the target for providing a firing signal when no Po ni-nw where I i d 7 r ilogPr) fis the-time derivative of the received infrared power and F and F 'are selected functions of launcher speedimissile: aerodynamic characteristics,,missilemaximum range,

ance with altitude and density ratio, and indicating means operatively connected to said computer means and having said firing signal applied thereto, said'indicating means utilizing the firing signal to provide a firing indication.

9min aircraft fire control system for use with a -honring type guided missile, in combination, infrared tracking-means adapted to lock on a targehtarget position indicator means for indicating to the pilot of the aircnaft the position of the target with respect to the instant heading of the aircrafh'first computing means operatively connected to said tracking means for computing a first signal having a value corresponding to the time derivative of the received infrared power second computing means operatively connected to said a tracking means for computing a second signal having a and at' least one atmosphere Conditionjin accordance with a altitude and dens-ityratio, and indicating mean 0Perative-' lyrconne'ctedto'sa'id computing means and having said Value Q SP iHgVtQ F +F (w) where F and F are 1 selected functions of launcher speed, missile aerodynamic characteristics, missile maximum; rangeand at least one atmosphere condition in "accordance with altitude and indioationrwhen said first and second signals attain equal value.

10. In an infrared missile fire control system, in combination, infrared energy responsive means for obtaining a first signal having an instant value corresponding to the value of at least one variable quantity needed to ascertain the earliest launching time of the missile, computing means operatively connected to the infrared energy responsive means for obtaining a second signal having an instant value corresponding to the value of a second variable quantity needed to ascertain the earliest launching time of the missile, and launching indication providing means operatively connected to said infrared energy responsive means and to said computing means and constructed and arranged to utilize the first and second signals to provide a launching indication.

11. In an aircraft missile fire control system in which the instant values of a plurality of variable quantities are obtained and utilized to ascertain the earliest firing time of the missile at a selected target in accordance with the normal maximum range of the missile as determined by its normal launching velocity at zero altitude from a fixed position at a fixed target, and said firing time is estimated upon the basis of the added velocity of the launcher aircraft, the range and range rate betwen launcher and target, the angular rate of the line of sight, and the effects of atmosphere conditions upon said missile, in combination, infrared energy responsive means for obtaining a variable signal corresponding to the instant value of a selected variable quantity which is a function of range and rangefrate, means for computing a second variable signal in accordance with variations in the instant value of a variable quantity which is a function of launcher speed, angular rate, and said atmosphere condition, and

means for comparing the values of said first and second signals to ascertain whether said firing time has occurred. 12. Inan aircraft missile fire control system in which the instant values of a plurality of variable quantities are 10 obtained and utilized to ascertain the earliest firing time of the missile at a selected target in accordance with the normal maximum rangeof the missile as determined by its normal launching velocity at zero altitude from a fixed position at a fixed target, and said firing time is estimated upon the basis of the added velocity of the launcher aircraft, the range and range rate betwen launcher and target, and the effects of atmosphere conditions upon said missile, in combination, infrared energy responsive means for obtaining a first variable signal corresponding to the instant value of a selected variable quantity which is a function of range and range rate, means for computing a second variable signal in accordance'with variations in the instant value of a variable quantity which is a function of launcher speed and said atmosphere condition, and means operatively connected to the infrared energy responsive means and to the computing means for utilizing said first and second signals to ascertain whether said firing time has occurred.

13. In an aircraft missile fire control system in which the instant values of a plurality of variable quantities are obtained and utilized to ascertain the earliest firing time of the missile at a selected target in accordance with the normal maximum range of the missile as determined by its normal launching velocity at zero altitude from a fixed position at a fixed target, and said firing time is estimated upon the basis of the added velocity of-the launcher aircraft, the range and range rate between launcher and target, the angular rate of the line of sight, and the effects of atmosphere conditions upon said missile, in combination, infrared energy responsive means for obtaining a variable signal corresponding to the instant value of a selected variable quantity which is a function of range and range rate, computing means, means operatively connected to said computing means for supplying inputs thereto corresponding to launcher speed, angular rate, and atmosphere condition, and means operatively connected to the infrared energy responsive means and to the computing means for providing an indication of said firing time.

References Cited in the file of this patent UNITED STATES PATENTS 2,377,589 Sutclifie June 5, 1945 

1. IN AN INFRARED MISSILE FIRE CONTROL SYSTEM, IN COMBINATION, FIRST COMPUTING MEANS RESPONSIVE TO INFRARED RADIATION RECEIVED FORM A TARGET FOR COMPUTING A FIRST SIGNAL HAVING A VALUE CORRESPONDING TO THE TIME DERIVATIVE OF THE RECEIVED INFRARED POWER 